KIEV, March 17 (Reuters) - Ukraine on Monday dismissed as "absolutely unacceptable" a Russian proposal to dispatch a "support group" to mediate in the crisis there and seek changes to the Ukrainian constitution.

"The statement of the Russian Foreign Ministry looks like an ultimatum," Ukrainian Foreign Ministry spokesman Yevhen Perebynis told the Interfax Ukraine news agency. "The position as set out is absolutely unacceptable for the Ukrainian side."

The Russian proposal, set out by the Foreign Ministry in Moscow, called for the creation of an international support group to mediate in the crisis.

The proposal also said the group should urge Ukraine to adopt a new constitution setting out broad powers for the country's regions and require Ukraine to uphold military and political neutrality.